The human stratum corneum, in which intercellular lipid forms a lamellar structure, is known to play an important role in barrier and moisturizing functions. Thus, in the production of skin agents for external application such as creams and emulsions, there is demand for a pharmaceutical product which enhances such functions and improves skin conditions.
From the viewpoint of enhancing barrier and moisturizing functions, a pharmaceutical product having the same lamellar structure as that of the skin is desired for the enhancement of skin permeability and moisturizing effect. Since the structure of a pharmaceutical product having a vesicle structure is similar to the structure of intercellular lipids in stratum corneum, such a pharmaceutical product is thought to have higher functions in terms of skin permeability, moisturizing effect, etc.
Hitherto, it has been known that vesicle compositions in which a continuous phase is an oily phase have been rarely employed. The only examples are a reverse vesicle formed of a nonionic surfactant, oil, and water (Non-Patent Document 1), and a water-free reverse vesicle containing sucrose monoalkanoate, hexaethylene glycerol hexadecyl ether, and heptane (Non-Patent Document 2).
However, reverse vesicle compositions having a lamellar structure have considerably poor stability, since the electrostatic repulsion force cannot be attained due to an oily continuous phase, which is problematic.    [Non-Patent Document 1]    Hironobu Kunieda et al., Langmuir, 1991, 7, 1915-1919    [Non-Patent Document 2]    Hironobu Kunieda et al., J. Phys. Chem., 1993, 97, 9525-9531